The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Speakers and speaker cabinets, and guitar speaker cabinets in particular, have long suffered from a tendency to project frequencies unevenly to an audience, such as performers, listeners, and microphones positioned in front of the speakers. With reference to FIG. 3A, a typical speaker mounted in a speaker cabinet, tends to project sound in a beam in front of the speaker cabinet. This beam has a central beam region 100, and outer beam regions 102A and 102B. In general, the higher frequencies, such as frequencies above one-thousand Hertz, present in the central beam region 100 are significantly greater in amplitude than the lower frequencies, such as those below one-thousand Hertz, present in that region. Conversely, the higher frequencies present in the outer beam regions 102A and 102B tend to be of lesser amplitude than the higher frequencies present in the central beam region 100. These higher frequencies present in the outer beam regions 102A and 102B also tend to more closely match the lower frequencies present in the outer beam regions 102A and 102B. As a result, the outer beam regions 102A and 102B are generally perceived by musicians, recording professionals, and others as having a more even tone than the central beam region 100.
Turning now to FIG. 5, a response curve 500 produced by placing the microphone close to the cabinet of FIG. 3A in the central beam region demonstrates the increased amplitude of higher frequencies in the central beam region. As a general rule, the higher the frequency, the more narrow the “beam” of that frequency that tends to be projected forward from the voice coil in the center of the speaker. This voice coil vibrates during operation, causing a conical membrane of the speaker that is attached to the voice coil to similarly vibrate. In contrast to the higher frequencies, lower frequencies tend to project forward from the entire conical membrane and disperse evenly in front of the speaker.
While response curve 500 extends from five-hundred Hertz to eight-thousand Hertz, it should be readily apparent to one skilled in the art that the range of human hearing extends from about twenty Hertz to about twenty-thousand Hertz. It should also be readily apparent that musical instruments, such as guitars, are typically only capable of playing notes in a range from about forty Hertz, in the case of a contra base guitar, to about one-thousand seven-hundred sixty Hertz, in the case of an alto guitar. However, musical instruments, and especially electric guitars, can produce higher frequencies as harmonic overtones, especially in the case of tube amp distortion for an electric guitar or use of artificial aural excitation for an electric/acoustic guitar. These harmonic overtones can easily range up to eight-thousand hertz. Thus, the presence of higher frequencies dramatically effects the tone of an amplified guitar signal.
Moreover, one skilled in the art will readily recognize that decibels are a logarithmic measure, and that perceived loudness of a sound is generally known to double with an increase of ten decibels. This perceived loudness does not directly relate to actual intensity or amplitude, which doubles with an increase of three decibels. Moreover, perceived loudness, which is an experimentally obtained psychoacoustic measure typically expressed in phons, does not directly correspond to decibels. Typically, a contouring filter, such as an A filter generally accepted for use in musical applications, can be applied to a rough conversion of decibels to phons, with the units expressed as dBA, dBB, or dBC, depending on the filter employed. Alternatively, a conversion table available in acoustics textbooks can be employed to achieve a more accurate conversion expressable as phons. However, the difference between decibels and phons or dBA is mostly significant for frequencies below one thousand Hertz and above eight thousand Hertz. For example, one skilled in the art will readily recognize that application of an A filter to curve 500 would leave points of the curve the same at one-thousand Hertz and five-thousand Hertz, while adjusting other frequencies between one-thousand and eight thousand Hertz by no more than about two decibels. Such application would, however, significantly reflect a decrease in the perceived loudness of lower frequencies below one-thousand Hertz. Accordingly, the difference between perceived loudness of the higher and lower frequencies is even more dramatic than might be otherwise reflected by curve 500.
The increased amplitude of the higher frequencies in the central beam region is generally referred to as “beaminess,” and has long been known to be an undesirable characteristic of speakers, and especially of guitar speaker cabinets, that causes various undesirable results. For example, audience members closer to the stage and positioned to receive the central beam experience “ice pick highs” or “sizzle” generally perceived as unpleasant. Also, recording professionals in the past have discovered that positioning a recording microphone in the central beam region produces undesirable results, and have learned to position the microphone in one of the outer beam regions. Similarly, live sound technicians, especially at larger venues, also need to mic one or more speakers of a guitar speaker cabinet for sound reinforcement through local PA systems. However, more often than not, these live sound technicians tend to place the microphone in the central beam region. As a result, the sound emanating from the PA system tends to be unbalanced, and the entire audience experiences the unpleasant “ice pick highs” or “sizzle.”
Turning now to FIG. 3B, attempts to reduce “beaminess” of a speaker cabinet have generally involved blocking the sound emanating from the central beam region 100. For example, others have tried placing a blocking member 106 composed of duct tape, felt, metal, fiber, and/or wood between the speaker and the audience in the central beam region 100. Typically, the blocking member 106 has been mounted inside the screen of the cabinet by attaching the blocking member 106 to the inside surface of the screen, or by providing one or more spokes extending from the cabinet baffle board on which the speaker is mounted, and attaching it to the spoke or spokes. Specifically, duct tape and/or felt discs have been attached to the screen, while wooden discs or metal and fiber discs have been mounted on spokes. Typically, the discs have been four to six inches in diameter for ten to twelve inch speakers, and slightly larger for fifteen inch speakers.
Returning now to FIG. 5, a response curve 502 produced by placing the microphone close to the blocked cabinet of FIG. 3B in the central beam region demonstrates the decreased amplitude of higher frequencies in the central beam region. Specifically, response curve 502 demonstrates the decreased amplitude of higher frequencies in the central beam region when a square section cut from a 2×4 wooden board made of pine is used as the blocking member 106. Low peaks 504A-504D in response curve 502 demonstrate that a perceptible “hole in the sound” exists for several of the higher frequencies in the central beam region when blocking is used. Blocking is known to be effective in reducing the “ice pick highs” received directly from the cabinet by audience members positioned in the central beam region. However, the “hole in the sound” is experienced by the audience in the central beam region. This “hole in the sound” is also experienced by the rest of the audience when live sound technicians inevitably place the microphone in the central beam region. As a result, most or all of the audience at a large venue experiences an unpleasantly “muddy” tone from the speaker being piped through the PA system of the venue.
Accordingly, the need remains for a way to reduce the unevenness, or “beaminess,” of a speaker without creating a perceptible “hole in the sound” in the central beam region. The present invention fulfills this need.